<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>Ruby Self: Ruby Study Notes - Best Ruby Guide, Ruby Tutorial</title>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<meta name="description" content="Ruby Study Notes - Best Ruby Guide, Ruby Tutorial" />
<meta name="keywords" content="ruby self,ruby study notes,free ruby programming guide,ruby guide,free ruby programming course,best ruby guide,ruby tutorials,ruby tutorial,learn ruby,ruby,ruby on rails,ruby rails,ruby learning,ruby tutoring,learning ruby,ruby programming,ruby on rails development,ruby training" />
<meta name="Distribution" content="Global" />
<meta name="author" content="Satish Talim / Original design: Erwin Aligam - ealigam@gmail.com" />
<meta name="copyright" content="Satish Talim 2007 and beyond..." />
<meta name="verify-v1" content="rFu86se+IkbtF+bH8mgJBKwU5HnKaSd8Ghw9umXQOkM=" />
<meta name="robots" content="index,follow" />
<meta http-equiv="Expires" content="0" />
<meta name="revisit-after" content="1 days" />
<link rel="stylesheet" href="/images/NewOrange.css" type="text/css" />
<link rel="stylesheet" href="/images/syntaxhighlighter.css" type="text/css" />
<link rel="icon" type="image/ico" href="/images/favicon.ico" />
<!-- Google +1 button code -->
<link rel="canonical" href="/satishtalim/ruby_self.html" />
<script type="text/javascript" src="https://apis.google.com/js/plusone.js"></script>

<!-- Google Analytics code -->
<script type="text/javascript">

  var _gaq = _gaq || [];
  _gaq.push(['_setAccount', 'UA-59044-10']);
  _gaq.push(['_trackPageview']);

  (function() {
    var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
    ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
    var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
  })();

</script>
<!-- Google Analytics code ends -->
</head>

<body>
<!-- wrap starts here -->
<div id="wrap">

    <div id="header">

        <h1 id="logo">Ruby<span class="orange">Learning.github.io</span></h1>
        <h2 id="slogan">Helping Ruby Programmers become Awesome!</h2>

    </div>

    <div id="menu">
        <ul>
            <li><a href="/" title="Home page for rubylearning.github.io">Home</a></li>
            <li><a href="/satishtalim/tutorial.html" title="Get started Learning Ruby here...">Tutorial</a></li>
            <li><a href="/download/downloads.html" title="Download this tutorial as an eBook">Downloads</a></li>
            <li><a href="/other/testimonials.html" title="People around the world who benefited from this site">Testimonials</a></li>
            <li><a href="/other/certification.html" title="Get certified in Ruby">Certification</a></li>
            <li><a href="/satishtalim/ruby_guide.html" title="Ruby Guide, Mentor">Mentor</a></li>
            <li><a href="https://blog.rubylearning.github.io/" title="Ruby blog of Learning Ruby site">Blog</a></li>
            <li><a href="/satishtalim/tutorial.html" title="Online Ruby Course">Online Course</a></li>
            <li><a href="http://ruby-challenge.rubylearning.github.io/" title="Ruby Programming Challenge for Newbies">Challenge</a></li>
            <li><a href="/satishtalim/about.html" title="Information about Satish Talim">About</a></li>
        </ul>
    </div>

    <!-- content-wrap starts here -->
    <div id="content-wrap">

            <div id="main">

                <div id="main-inner"><a name="TemplateInfo"></a>
                <h1>Self - The current/default object</h1>

                <p class="post-footer align-right">
                  <strong>
                    <a href="/satishtalim/modules_mixins.html">&lt;Modules/Mixins | </a>
                    <a href="/satishtalim/tutorial.html">TOC | </a>
                    <a href="/satishtalim/ruby_constants.html">Constants &gt;</a>
                  </strong>
                </p>

                <p>At every point when your program is running, there is <em>one and only one</em> <strong>self</strong> - the current or default object accessible to you in your program. You can tell which object <strong>self</strong> represents by following a small set of rules.</p>

                <h3>Top level context</h3>

                <p>The top level context is before you have entered any other context, such as a class definition. Therefore the term top level refers to program code written outside of a class or module. If you open a new text file and type:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                x = 1
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>you have created a top level local variable x. If you type:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                def m
                end
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>you have created a top level method - an instance method of <strong>Object</strong> (even though <strong>self</strong> is not <strong>Object</strong>). Top-level methods are always private. Ruby provides you with a start-up <strong>self</strong> at the top level. If you type:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                puts self
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>it displays <strong>main</strong> - a special term the default <strong>self</strong> object uses to refer to itself. The class of the <strong>main</strong> object is <strong>Object</strong>.</p>

                <h3>Self inside class and module definitions</h3>

                <p>In a class or module definition, <strong>self</strong> is the class or module object.</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                # p063xself1.rb
                class S
                  puts 'Just started class S'
                  puts self
                  module M
                    puts 'Nested module S::M'
                    puts self
                  end
                  puts 'Back in the outer level of S'
                  puts self
                end
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>The output is:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                >ruby p063xself1.rb
                Just started class S
                S
                Nested module S::M
                S::M
                Back in the outer level of S
                S
                >Exit code: 0
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <h3>Self in instance method definitions</h3>

                <p>At the time the method definition is executed, the most you can say is that <strong>self</strong> inside this method will be some future object that has access to this method.</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                # p063xself2.rb
                class S
                  def m
                    puts 'Class S method m:'
                    puts self
                  end
                end
                s = S.new
                s.m
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>The output is:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                >ruby p063xself2.rb
                Class S method m:
                #&lt;S:0x2835908&gt;
                >Exit code: 0
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>The output #&lt;S:0x2835908&gt; is Ruby's way of saying "an instance of S".</p>

                <h3>Self in singleton-method and class-method definitions</h3>

                <p><em>Singleton methods</em> - those attached to a particular object can be called by only one object. When a singleton method is executed, <strong>self</strong> is the object that owns the method, as shown below:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                # p063xself3.rb
                obj = Object.new
                def obj.show
                  print 'I am an object: '
                  puts "here's self inside a singleton method of mine:"
                  puts self
                end
                obj.show
                print 'And inspecting obj from outside, '
                puts "to be sure it's the same object:"
                puts obj
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>The output of the above example is:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                >ruby p063xself3.rb
                I am an object: here's self inside a singleton method of mine:
                #&lt;Object:0x2835688&gt;
                And inspecting obj from outside, to be sure it's the same object:
                #&lt;Object:0x2835688&gt;
                >Exit code: 0
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>Class methods are defined as singleton methods for class objects. Refer to the following program:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                # p063xself4.rb
                class S
                  def S.x
                    puts "Class method of class S"
                    puts self
                  end
                end
                S.x
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p>The output is:</p>

                <div class="column2">
                <!-- InstanceBeginEditable name="Code" -->
                <textarea name="code" class="ruby:nogutter:nocontrols" rows="15" cols="60">
                >ruby p063xself4.rb
                Class method of class S
                S
                >Exit code: 0
                </textarea>
                <!-- InstanceEndEditable -->
                </div>

                <p><strong>self</strong> inside a singleton method (a class method, in this case) is the object whose singleton method it is.</p>

                <p style="background-color: #FAFAFA; padding: 5px; margin-top: 20px; font-size: 65%;"><strong>Note</strong>: The Ruby Logo is Copyright (c) 2006, Yukihiro Matsumoto. I have made extensive references to information, related to Ruby, available in the public domain (wikis and the blogs, articles of various <span style="font-weight: bold;" title="Click Gurus on the menu above">Ruby Gurus</span>), my acknowledgment and thanks to all of them. Much of the material on <a href="/">rubylearning.github.io</a> and in the course at <a href="http://rubylearning.org/">rubylearning.org</a> is drawn <strong>primarily</strong> from the <strong>Programming Ruby book</strong>, available from <a href="http://pragprog.com/titles/ruby3/programming-ruby-3">The Pragmatic Bookshelf</a>.</p>

                <p class="post-footer align-right">
                  <strong>
                    <a href="/satishtalim/modules_mixins.html">&lt;Modules/Mixins | </a>
                    <a href="/satishtalim/tutorial.html">TOC | </a>
                    <a href="/satishtalim/ruby_constants.html">Constants &gt;</a>
                  </strong>
                </p>

            </div>
            <!-- main inner ends here -->
        </div>

            <div id="rightbar">

            </div>

    <!-- content-wrap ends here -->
    </div>

<!-- wrap ends here -->
</div>

<!-- footer starts here -->
<div id="footer">
    <!-- CHANGE THE FOOTER -->
    <p>&copy; 2006-2021 <strong>rubylearning.github.io - A Ruby Tutorial</strong>&nbsp;&nbsp;Page Updated: 5th Jan. 2021 | Design: <a href="mailto:ealigam@gmail.com">Erwin Aligam</a> | Valid: <a href="http://validator.w3.org/check/referer">XHTML</a> | <a href="http://jigsaw.w3.org/css-validator/check/referer">CSS</a>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href="/">Home</a> | <a href="/privacy.html">Privacy</a> | <a href="/sitemap.html">Sitemap</a></p>
</div>

<!-- footer ends here -->

<!-- SyntaxHighlighter code -->
<script src="/js/shCore.js" type="text/javascript"></script>
<script src="/js/shBrushRuby.js" type="text/javascript"></script>
<script type="text/javascript">
dp.SyntaxHighlighter.HighlightAll('code');
</script>
<!-- SyntaxHighlighter code -->

</body>
</html>
